The invention relates to a variable focus lens, and to spectacles using the variable focus lens. It also extends to certain types of spectacles using other variable focus lenses.
One type of prior art variable focus lens is disclosed, for example, in GB 2333858. This lens is formed from several interengaging rings. Flexible transparent membranes are trapped between the rings, and the rings are formed such that as they interengage, they tension the flexible membranes (which improves the performance of the lens). One of the rings is then deformed to hold the assembly together. However, this design places certain requirements (such as-ductility) on the materials used to form the rings, and also requires strict tolerances in the manufacturing of the rings. Further, each lens is formed from a large number of separate parts, which complicates manufacture.